1. Field of the Invention
The present invention relates to a ferromagnetic film suitable for a magnetic head and the like.
2. Description of the Related Art
Generally, a magnetic film for a magnetic head is required to have high saturation magnetic flux density (high Bs) and soft magnetic characteristics, e.g., low coercive force (low Hc), so that it can have a sufficient recording capability for a recording medium having high coercive force (high Hc).
Although Fe-, Co- and FeCo-based alloys exhibit high Bs, they have undesirably high Hc because of a large magnetocrystalline anisotropy. Therefore, it is difficult to obtain excellent soft magnetic characteristics suitable for a magnetic head and the like. Although FeAlSi and NiFe alloy films obtained by adding additives to above alloys, thereby setting the magnetocrystalline anisotropy close to zero, exhibit low Hc, their saturation magnetic flux density Bs is as low as 1.1 tesla (T) at maximum. Although many Fe- and Co-based alloys exhibit low Hc when they are made amorphous, the saturation magnetic flux density Bs of those that can be put into practical use considering their heat resistance is as low as 1.0 T at maximum.
Nevertheless, even a film having a large magnetocrystalline anisotropy can be set to exhibit low Hc theoretically by controlling its crystal orientation. More specifically, an fcc (111) oriented magnetic film exhibits low Hc since the influence of a magnetocrystalline anisotropy constant K.sub.1 can be neglected within the film plane. For example, a bcc-phase Fe solid solution exhibits the (111) orientation and low Hc by selecting an appropriate underlying substrate, e.g., FeSi/ZnSn (Hosono et al., J. Appl. Phys., 67, 6990 (1990)). The Fe-based alloy, however, usually exhibits the (100) or (110) orientation because the bcc phase is stable. The (111) orientated film is hard to grow stably other than on a specific substrate such as ZnSe because it has a large surface energy.
In the case of a Co-based alloy with a composition near Co.sub.90 Fe.sub.10 having Bs of about 1.9 T, it is confirmed from the phase diagram that the fcc phase stably exists in the alloy. In the fcc phase, the (111) plane is a stably growing plane owing to low surface energy. In fact, however, it is difficult to obtain the high (111) orientation even in such an alloy film.
A magnetic film obtained by adding a transition metal, e.g., zr or Ta, and nitrogen to Fe or Co is promising for a magnetic recording head in the future because it has high Bs and its soft magnetism is not degraded by heat. In addition, when considering the practical applicability in a high-humidity atmosphere containing chlorine, a Co-based magnetic film may be suitable since an Fe-based magnetic film does not have a sufficiently high corrosion resistance.
As Co-based nitrogen-added films, a nitrogen-content modulated film having a multilayered structure (IEEE Trans. Magn., 23, 3707 (1987)), a CoNbZrN film (J. Appl. Phys., 68, 4760 (1990)), a CoFeAlN film which has been studied by the present inventors (Preprint of meeting of the 14th Japan Applied Magnetics Society, 292 (1990)), and the like are known. Each of these magnetic films is known to have low Hc of 80 A/m or less equivalent to that of a conventional magnetic film and exhibits excellent soft magnetism.
However, these magnetic films have the following drawbacks. The nitrogen-content modulated film maintains its soft magnetism up to about 700.degree. C. and exhibits a considerably high heat resistance. However, its manufacturing process is complicated since it has a multilayered structure. In contrast to this, the CoNbZrN and CoFeAl films are easy to manufacture since they have a single-layered structure. However, when these magnetic films are annealed at 400.degree. C. or more, crystal growth gradually proceeds in them to cause an increase in Hc and a decrease in resistivity. Especially, when these magnetic films are applied to a laminated head that employs a high-temperature manufacturing process at 600.degree. C. or more, an increase in Hc accompanying the crystal growth poses a serious problem. In addition, the decrease in resistivity causes an degradation of the RF characteristics due to an increase in eddy currents. A CoNbZrN film manufactured by ion beam sputtering exhibits excellent characteristics. However, a CoNbZrN manufactured by conventional RF magnetron sputtering does not always exhibit excellent characteristics since a perpendicular magnetic anisotropy tends to occur easily, resulting in a small manufacturing margin. Regarding the CoFeAlN film, it does not have a sufficient corrosion resistance in water.
As described above, although the CoFe-based alloys have high saturation magnetic flux density of 1.9 T or more, they have a large magnetocrystalline anisotropy and cannot realize high (111) orientation. Therefore, it is difficult to achieve sufficiently low Hc suitable for a magnetic film of a head magnetic pole.
Regarding the magnetic films obtained by adding a transition metal such as Zr or Ta and nitrogen to a ferromagnetic metal such as Co, when they are annealed at a high temperature, crystal growth gradually proceeds in them to cause an increase in Hc and a decrease in resistivity, resulting in an insufficient heat resistance. When these films are manufactured by conventional RF magnetron sputtering, a perpendicular magnetic anisotropy tends to occur easily, and therefore it is difficult to obtain excellent soft magnetism.